ctools

When running ctselect using an XML file on input that contains a single observation, two output files are created, one containing the XML descriptor for the selected event file, and the other containing the selected events file.

However, this even happens when the output file is called selected_events.fits. In this case, two files will be written, one named selected_events.fits and the other selected_something.fits. One gets the impression that now 2 FITS files exist, but the file selected_events.fits is in fact a XML file.

This is disturbing. We could imagine that we check the file name extension to guess the users intention, but this would mean that the behaviour of ctselect depends implicitly on the file name extension. This is also error prone.